(1) Field of the Invention
The present invention generally relates to a mechanical torque transmitting device and more particularly to clutches which allow rotation in one direction and resist rotation in the opposite direction.
(2) Prior Art
The use of one-way clutches for controlling the motion of one or more movable members is well known in the prior art. Such clutches generally allow the controlled member to rotate freely in one direction, called the free-wheeling direction, but resist motion in the non free-wheeling direction. The use of such devices is so well known that a detailed description of each of the prior art, to be listed hereinafter, is merely cumulative and adds nothing to enlighten a skilled artisan regarding the prior art. In view of this notoriety, only a listing of the prior art is given without a detailed description of each of the cited references. U.S. Pat. Nos. 2,075,130; 2,601,911; 3,130,826; 3,200,918; 3,386,122; 3,429,523; 3,459,390; 3,486,597; 3,589,486; 3,814,223; 3,928,862; 3,946,843; 4,044,868; and 4,346,729 are examples of the prior art clutches.
Of the cited prior art, U.S. Pat. Nos. 3,589,486 and 3,946,843 are representative of the various types of prior art clutches. More specifically, U.S. Pat. No. 3,589,486 represents the so-called toothed pawl type clutches while U.S. Pat. No. 3,946,843 represents the non-toothed pawl.
The toothed pawl type clutches (exemplified by U.S. Pat. No. 3,589,486) has an annular outer member with inner ratchet teeth and an inner member having a plurality of resilient arms with pawl-end portions which resiliently engage the ratchet teeth and recesses of the outer member. Each arm has an elongated thin portion extending substantially in a circumferential direction along the ratchet teeth so that the arms can be bent by the ratchet teeth in radial direction during relative turning of the inner and outer members in one direction, but slippage-free and resiliently couple the inner and outer members during relative movement in the opposite direction due to the fact that the ratchet teeth apply pressure in circumferential direction to the circumferentially extending arm portions.
U.S. Pat. No. 3,946,843 represents the non-toothed pawl type clutches. The clutch consists of a cylindrical engagement surface and one or more disc elements carrying members extending therefrom and flexibly attached thereto. The members are adapted to edgewise frictionally engage the cylindrical surface so that relative motion between the cylindrical surface and the disc elements in one direction causes frictional slippage of the members and relative motion in the opposite direction causes light driving engagement.
Other types of clutches such as roller, spring, locking arm and metal strap are well represented in the above enumerated patents. However, the existence and theory of operation of these clutches are well known and a further description will not be given.
Although the above prior art clutches work well for their intended purpose, they are plagued by several problems. One of the general problems which affects the prior art cluthes is that these clutches consist of a single set of arms which is used to meet all requirements of locking in one direction and free wheeling in the other. As used herein, a set may include one or more members. The requirements for each of the two operations are inapposite. For example, in the free-wheeling direction, the locking force between the set of arms and the rotating members should be at a minimal value. Conversely, in the non free-wheeling direction, the force should be at a maximum value. Because of these inapposite requirements, it is difficult to maximize the allowable locking force before breakage and it is difficult to minimize the free-wheeling resisting force.
Other general problems which beset the prior art clutches are that these clutches consist of numerous working parts, difficult to manufacture, low angular resolution, high free-wheeling friction, and low allowable lock force.